The invention relates to an apparatus for recording and/or playing back signals on a magnetic tape carried on two rotatable spools in a cassette and passed over a movable tape guide. The invention relates particularly to a recording and/or playback apparatus of the kind (hereinafter referred to as a helical scan tape recorder) comprising a deck plate, means for supporting the cassette on the deck plate, means for driving one of the spools in the cassette to wind the tape onto that spool and unwind it from the other spool, a rotary magnetic recording and/or playback head supported for rotation relative to the deck plate, a guide drum for the tape, which drum is supported on the deck plate with its axis coinciding with the axis of rotation of the rotary magnetic head, and tape guide means for pulling part of the tape between the spools out of the cassette and laying it on the cylindrical surface of the guide drum and for subsequently guiding the tape along a helical path around part of the cylindrical surface of the drum so that the rotary magnetic head can record and/or play back signals on the tape which are arranged in tracks extending obliquely relative to the longitudinal direction of the tape.
The term "guide drum" is to be understood herein to include a drum composed of separate coaxial parts.
In a known apparatus of the above kind which is described in German Offenlegungsschrift No. 27 19 746, the second position of the tape guide element is defined by a stop member mounted on the deck plate. This stop member is provided with three different stops for determining the position of the tape guide element on the stop member. These stops, together with corresponding parts of the tape guide element, define the height and angular position of the element relative to the deck plate. One stop is constituted by a V-shaped recess, a second stop by a U-shaped recess and a third stop by a contact surface. Such a device for positioning a tape guide is comparatively complicated, and the three stops situated on the stop member have to be mounted very accurately relative to each other. Generally, the positional accuracy of the tape guide element when it has been moved into the second position is extremely important because the position of this tape guide element determines the path of the magnetic tape relative to other parts of the apparatus, specifically the magnetic heads, past which parts the magnetic tape must travel in a very accurately defined direction and angular position.